JPH10103132A - Air-fuel ratio control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To delay rich/lean inversion decision in air-fuel ratio feedback control, in the case of starting feedback correction after sensor activation, start the air-fuel ratio feedback correction during the delay time of rich/lean inversion division, and prevent generation of fluctuation of air-fuel ratio. SOLUTION: In rich/lean inversion decision when a sensor output is generated higher/lower than a rich/lean decision value (0.45V), a delay time TLR, TRL is set. Air-fuel ration feedback correction is started after activation of an O2 sensor, this activation decision is performed by whether or not a sensor output is an activation decision value (0.55V) or more. However, the air-fuel ratio feedback correction is not executed after a transfer to activation from non- activation of an O2 sensor till the lapse of prescribed period TA (TA>=TLR).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the rich lean air-fuel ratio output is compared with a predetermined rich-lean determination value of the oxygen concentration sensor for detecting oxygen concentration in the exhaust gas of the engine (O ₂ sensor) The present invention relates to an air-fuel ratio control device for an engine that performs a determination, sets a predetermined air-fuel ratio feedback correction value based on the determination, and performs feedback correction of a fuel injection amount and the like based on the correction value.

[0002]

The air-fuel ratio control of an engine, is placed an oxygen concentration sensor (O ₂ sensor) for detecting the oxygen concentration in the exhaust gas in the exhaust system of the engine, a predetermined rich-lean determination value that sensor output It is usual to make a rich / lean determination of the air-fuel ratio by comparison, set a predetermined air-fuel ratio feedback correction value based on the determination, and perform feedback correction of the fuel injection amount. In such a feedback-type air-fuel ratio control, a predetermined delay time is set for the rich / lean reversal determination when the sensor output goes above or below the predetermined rich / lean determination value, thereby setting the air-fuel ratio. Conventionally, there has been known one in which the stoichiometric air-fuel ratio at the excess air ratio λ = 1 is slightly corrected to a rich side or a lean side. The one described in JP-B-58-44845 is one example. Setting the delay time for the rich / lean reversal determination as described above is advantageous, for example, when the air-fuel ratio is slightly shifted to the rich side to reduce nitrogen oxides (NOx).

The feedback correction of the air-fuel ratio control usually starts after the engine starts and after the temperature rises and the O ₂ sensor is activated. And the activity judgment is O
Usually, the determination is made based on whether the output of the _two sensors is equal to or greater than a predetermined activity determination value.

[0004]

As described above, the feedback correction of the air-fuel ratio control is started after the engine starts and after the temperature rises and the O ₂ sensor is activated.
At this time, it is usual to determine the activation based on whether or not the output of the O ₂ sensor is equal to or greater than a predetermined activation determination value. However, in the case of setting a predetermined delay time for the rich / lean inversion determination, for example, the activation determination The value is set to a value equal to or greater than the rich / rich determination value, and when the sensor output is equal to or greater than the activation determination value and the air-fuel ratio feedback correction is started after starting, the sensor output is equal to or greater than the rich / lean determination value. When the delay time before the rich / lean determination is reversed after the condition
Despite the output of the _two sensors having already shifted to the rich side, correction in the rich direction is performed while maintaining the lean determination, and as a result, the air-fuel ratio fluctuates.

[0005] In addition, for example, when the engine is in an idling operation state even after the start, the exhaust gas temperature is low and the O
₍₂₎ The output of the sensor may enter the inactive region.In such a case, when the sensor output again becomes equal to or greater than the activation determination value and the air-fuel ratio feedback is started, the sensor output becomes equal to or greater than the rich / lean determination value. After that, if the delay time before the rich / lean determination is reversed does not end yet, the output of the O ₂ sensor may actually be rich even though the output has already shifted to the rich side. Correction in the rich direction is performed with the judgment as it is,
The air-fuel ratio fluctuates.

The activation of the O ₂ sensor is slow, and the
If the sensor output does not exceed the activation determination value within the delay time of the lean reversal determination, the above-described problem does not occur. However, for example, in the case where a catalyst device is arranged at or near the exhaust manifold and an O ₂ sensor is arranged upstream of the catalyst device, the temperature of the O ₂ sensor rises quickly, and the delay of the rich / lean reversal determination is delayed. The sensor output may become equal to or higher than the activation determination value before the time elapses, and in such a case, the above-described problem occurs.

Therefore, the sensor output of the O ₂ sensor is compared with a predetermined rich / lean determination value to determine the rich / lean air-fuel ratio.
In the feedback-type air-fuel ratio control in which a lean determination is performed, a predetermined air-fuel ratio feedback correction value is set based on the determination, and feedback correction is performed, a predetermined delay time is set for rich / lean reversal determination, and a sensor output is set. When the air-fuel ratio feedback correction is started after is greater than or equal to the activation determination value, the delay time from when the output of the O ₂ sensor actually shifts to the rich side or lean side until the rich / lean determination is reversed Another problem is to prevent air-fuel ratio fluctuation due to the start of air-fuel ratio feedback correction.

[0008]

The above object can be attained by starting the execution of the air-fuel ratio feedback correction after a lapse of a predetermined period from the determination that the O ₂ sensor has shifted to the active state. . Therefore, air-fuel ratio adjusting means for adjusting the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the engine, operating state detecting means for detecting a predetermined state quantity relating to the operating state of the engine, and Control amount setting means for setting a control amount of the air-fuel ratio adjusting means on the basis of an oxygen concentration sensor for detecting an oxygen concentration in the exhaust gas of the engine, and comparing the sensor output with a predetermined rich / lean determination value Rich-lean determination means for determining whether the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the engine is richer or leaner than the stoichiometric air-fuel ratio,
Inversion delay means for setting a predetermined delay time for the rich / lean inversion determination; and a predetermined air-fuel ratio for converging the engine air-fuel ratio to a predetermined target air-fuel ratio based on the determination after the delay by the inversion delay means. An air-fuel ratio control device that sets a feedback correction value and corrects a control amount by the air-fuel ratio feedback correction value. Oxygen concentration sensor activity determination means for determining that the oxygen concentration sensor is in the active state, and correction for delaying the execution of the air-fuel ratio feedback correction so as to start after a predetermined period has elapsed after it is determined that the oxygen concentration sensor has shifted to the active state. An execution delay unit is provided. By doing so, when the sensor output enters the active region from the inactive region at the time of startup or during the idle operation state, the air-fuel ratio feedback correction is not immediately started but is started after a predetermined period has elapsed. . Therefore, after the sensor output becomes equal to or greater than the rich / lean determination value, the feedback correction in the rich direction due to the lean determination until the predetermined delay time elapses and the rich / lean determination is reversed to the rich side is suppressed, and the idle correction is performed. Fluctuations in fuel ratio are prevented.

In this case, it is preferable that the activation determination value is a value equal to or greater than the rich / lean determination value, and the predetermined period is set within the predetermined delay time. By doing so,
The air-fuel ratio feedback correction can be started immediately after the O ₂ sensor is sufficiently activated and the delay time has elapsed.

[0010] Another object of the present invention is to execute the air-fuel ratio feedback correction after it is determined that the oxygen concentration sensor has shifted to the active state and when the rich / lean determination is actually performed from the lean side to the rich side. This can be solved by starting after the transition. For this purpose, the same air-fuel ratio adjusting means, operating state detecting means, control amount setting means, oxygen concentration sensor, rich / lean determining means,
In an air-fuel ratio control device for an engine, comprising an inversion delay unit and an air-fuel ratio feedback correcting unit, an oxygen concentration sensor activity determination that determines that the oxygen concentration sensor is in an active state when the sensor output is equal to or greater than a predetermined activity determination value Means for performing the correction so that the execution of the air-fuel ratio feedback correction is started after the oxygen concentration sensor is determined to have shifted to the active state and after the determination after the delay has shifted from the lean side to the rich side. A delay means is provided. By doing so, when the sensor output enters the active region from the inactive region at the time of starting or during the idling operation state, the air-fuel ratio feedback correction is not immediately started, and the air-fuel ratio feedback correction is performed immediately after the predetermined delay time has elapsed. -It is started after the lean judgment shifts from the lean side to the rich side. Therefore, the feedback correction in the rich direction by the lean determination until the rich / lean determination is reversed to the rich side after the predetermined delay time has elapsed is eliminated, and the fluctuation of the air-fuel ratio is prevented.

The above-mentioned problem is also solved by executing the air-fuel ratio feedback correction after it is determined that the oxygen concentration sensor has transitioned to the active state, and when the output of the oxygen concentration sensor is greater than a predetermined rich / lean determination value. The problem can be solved by shifting from the lean side to the rich side and starting after a predetermined period has elapsed. For this purpose, an air-fuel ratio adjustment unit, an operation state detection unit, a control amount setting unit, an oxygen concentration sensor, a rich / lean determination unit, a reversal delay unit, and an air-fuel ratio feedback correction unit are provided. An oxygen concentration sensor activity determining means for determining that the oxygen concentration sensor is in an active state when an output of the oxygen concentration sensor is equal to or more than a predetermined activity determination value, and executing air-fuel ratio feedback correction. After the oxygen concentration sensor is determined to have transitioned to the active state, and after a predetermined period has elapsed after the output of the oxygen concentration sensor has shifted from the lean side to the rich side from a predetermined rich / lean determination value. A correction execution delay means for delaying the start is provided.
By doing so, when the sensor output enters the active region from the active inactive region at the time of starting or during the idle operation state, the air-fuel ratio feedback correction does not start immediately, and the output of the oxygen concentration sensor becomes a predetermined value. The process is started after a predetermined period elapses from the lean side to the rich side with respect to the rich / lean determination value. Therefore, after the sensor output becomes equal to or greater than the rich / lean determination value, the feedback correction in the rich direction due to the lean determination until the predetermined delay time elapses and the rich / lean determination is reversed to the rich side is suppressed, and the empty state is suppressed. Fluctuations in fuel ratio are prevented.

FIG. 1 shows the overall configuration of the present invention.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an overall engine system to which the present invention is applied. In the figure, reference numeral 1 denotes a spark ignition type engine. The engine 1 includes a cylinder block 3 having an in-line multi-cylinder cylinder bore 2, a cylinder head 4 connected to an end face of the cylinder block 3, and a cylinder bore 2.
The combustion chamber 6 is formed between the top surface of the piston 5 in each cylinder bore 2 and the inner surface of the cylinder head 4. The cylinder head 4 is provided with two intake ports 7a and 7b and two exhaust ports 8a and 8b so as to open to the combustion chamber 6 of each cylinder. The cylinder head 4 is provided with intake valves 9, 9 for opening and closing the combustion chamber 6 openings of the intake ports 7a, 7b, and opening and closing the combustion chamber 6 openings of the exhaust ports 8a, 8b. Exhaust valves 10 and 10 are provided.

The cylinder head 4 has a combustion chamber 6 for each cylinder.
An intake passage 11 is connected so as to introduce an air-fuel mixture into the intake ports 7a and 7b, and an exhaust passage 12 is connected so as to lead the exhaust gas discharged from the exhaust ports 8a and 8b. An air cleaner 13 that cleans and filters the intake combustion air, an air flow meter 14 that detects the amount of intake air, a throttle valve 15 that adjusts the amount of intake air, A surge tank 16 for absorbing pulsation of intake air, a boost sensor 17 for detecting intake negative pressure (boost), and a fuel injection valve 18 are sequentially arranged.

In the intake passage 11, downstream of the surge tank 16 is an independent intake passage 19 for each cylinder. As shown in the schematic diagram of FIG. 3, each of the independent intake passages 19 for each of the cylinders has a first passage 19a and a second passage 19a on the downstream side.
b, the first passage 19a is connected to one of the intake ports 7a.
The second passage 19b is connected to the other intake port 7b. A swirl control valve 20 is provided in the first passage 19a connected to the one intake port 19a, and the fuel injection valve is provided in the second passage 19b connected to the other intake port 19b. 18 are provided.

The exhaust passage 12 is provided with an exhaust purification catalytic converter 21 directly attached to the manifold, and a sensor output linearly changes upstream of the catalytic converter 21 in accordance with the oxygen concentration in the exhaust gas. A linear O ₂ sensor 22 has a λ downstream of the catalytic converter 21.
The λO ₂ sensor 23 whose output changes rapidly when (excess air ratio) = 1 is provided.

A bypass passage 24 is provided in the intake passage 11 to supply bypass air bypassing the throttle valve 15 during idling operation.
In the middle of 4, a duty solenoid valve 25 for adjusting the amount of bypass air and controlling the engine speed during idling is provided.

The cylinder head 4 of the engine 1 is provided with an ignition plug 26 at a position facing the combustion chamber 6 of each cylinder, and an igniter 27 for generating a high voltage required for ignition and a crankshaft ( (Not shown), a distributor 28 for distributing and supplying the high voltage generated by the igniter 27 to the ignition plug 26 of each cylinder is provided. The distributor 28 is provided with an engine rotation sensor 29 for generating a pulse signal according to the rotation of the crankshaft. The throttle valve 15 is provided with an idle switch 30 for detecting that the throttle is fully closed. Further, an intake air temperature sensor 31 for detecting the temperature of the intake air is provided, and a water temperature sensor 32 for detecting the temperature of the engine cooling water is provided.

The engine 1 has a control unit 33 composed of a microcomputer. The control unit 33 includes an engine rotation sensor 29,
In addition to the air flow sensor 14, the idle switch 30, the intake air temperature sensor 31, the water temperature sensor 32, the linear O ₂ sensor 22 and the λ O ₂ sensor 23, various signals output from the vehicle speed sensor 34, the catalyst temperature sensor 35 and the like are input.
The control unit 33 controls the fuel injection valve 18 based on these signals, controls the swirl control valve 20, and controls the duty solenoid valve 25 of the bypass passage 24.

In the control of the fuel injection valve 18, a basic injection amount is calculated based on the engine speed and the intake air amount, and various corrections such as a water temperature correction are added thereto. Further, in the air-fuel ratio feedback region set in advance according to the engine operating state, the air-fuel ratio feedback correction is applied to the fuel injection amount so that the air-fuel ratio detected by the linear O ₂ sensor 14 upstream of the catalyst matches the target air-fuel ratio. Then, the fuel injection valve 18 is operated by an injection pulse signal corresponding to the set final injection amount, and fuel is injected based on the pulse width.
The air-fuel ratio is feedback-controlled to the target air-fuel ratio. Also,
Close the swirl control valve in the low rotation range when cold,
In all other conditions, open the swirl control valve. This control is to reduce the emission of unburned components (HC) during cold periods, and when the swirl control valve is open,
Fuel is injected before the intake stroke period, the injection timing is advanced as the engine speed increases, and when the swirl control valve is closed, the fuel injection timing is set so as to inject fuel during the intake stroke period. Control.

In the air-fuel ratio feedback correction, the sensor output of the O ₂ sensor 22 is compared with a predetermined rich / lean determination value to make a rich / lean determination of the air-fuel ratio, and based on the determination, a predetermined air-fuel ratio feedback correction value is obtained. Is set, and the fuel injection amount is feedback-corrected. At this time, as shown in FIG. 4, the rich / lean inversion determination when the sensor output is increased or decreased by a predetermined rich / lean determination value (for example, 0.45 V) A predetermined delay time T _LR (for a lean-to-rich reversal) and T _RL (for a rich-to-lean reversal) is set, thereby reducing the air-fuel ratio to a stoichiometric air with an excess air ratio λ = 1. The fuel ratio is slightly shifted to the rich side to reduce nitrogen oxides (NOx). The air-fuel ratio feedback correction is started after the O ₂ sensor 22 is activated, and the activation is determined based on whether the sensor output is equal to or greater than a predetermined activation determination value (for example, 0.55 V). However, the air-fuel ratio feedback correction is performed after the O ₂ sensor 22 shifts from inactive to active.
It is not executed until a predetermined period T _A (T _A ≧ T _LR ) has elapsed, so that when the sensor output enters the active region from the inactive region at the time of starting or during the idling operation state, the air-fuel ratio without immediately executing the feedback correction, after the delay time T _LA rich lean inversion determination has elapsed, so as to start execution, suppressing feedback correction to the rich direction between the delay time T _LA, the air-fuel ratio We try to prevent fluctuations.

[0023] For example, during startup, when the sensor output becomes the activity judgment value or more, when the delay time T _LR rich lean inversion determination has not ended, rich lean determination remains the determination leaner However, the actual output of the O ₂ sensor 22 has already shifted to the rich side, and when the air-fuel ratio feedback correction is executed in such a situation, the correction in the rich direction is performed even though the air-fuel ratio is already on the rich side. The result is that the air-fuel ratio fluctuates. In addition, even when the engine is not started, for example, the idling state continues and the O ₂ sensor 2
2 may enter the inactive region, a similar phenomenon occurs when the sensor output again becomes equal to or higher than the activation determination value,
The air-fuel ratio fluctuates. In the case where the O ₂ sensor 22 is arranged upstream of the catalytic converter 21 directly attached to the manifold,
The activation is fast, the rising of the sensor output is fast as shown by A in FIG.
Before the _LR elapses, the sensor output may exceed the activation determination value, and in such a case, the above-described phenomenon occurs. However, when the control for delaying the start of the execution of the air-fuel ratio feedback correction by the predetermined period T _A is performed, the execution of the air-fuel ratio feedback correction is delayed by the predetermined period T _A , and the delay time T _LR of the rich / lean inversion determination elapses. After doing this, FIG.
Thus, the above-mentioned problem does not occur. Incidentally, as shown by B in FIG. 4, if the rise of the sensor output is gradual and the sensor output becomes equal to or greater than the activation determination value after the delay time T _LR of the rich / lean inversion determination has elapsed, If the execution of the air-fuel ratio feedback correction is started immediately at the time point b when the sensor output exceeds the activation determination value, no problem occurs.

FIGS. 5 to 7 show flowcharts for executing the air-fuel ratio feedback control in the above embodiment.

First, FIG. 5 shows a routine executed when the engine is started. In step S101, it is determined whether or not the engine is started. When it is determined that the engine is started, the process proceeds to start S102, and the flags and counters are initialized. Set to.

FIG. 6 shows O ₂ executed by a time synchronous interrupt.
This is a sensor activity determination routine. When started, the sensor output OX ₀ of the O ₂ sensor is read in step S 201, and in step S 202, the activity is determined based on whether the sensor output OX ₀ is equal to or more than the activity determination value 0.55 V. If OX ₀ is not 0.55 V or more, the routine returns.

On the other hand, when OX ₀ is 0.55 V or more,
O ₂ sensor that the now active, the process proceeds to step S203, increments the counter T ₁ by one.

Next, at step 204, the counter T
₁ determines whether equal to or more than the predetermined time period T _A. Then, T ₁ is the time in the T _A, to return as it is.

When the counter T ₁ has become equal to or longer than the predetermined period T _A , the counter T ₁ is returned to 0 in step S205, and then the O ₂ sensor activation flag F is set to 1 in step S206.

FIG. 7 shows a fuel injection control routine executed by interruption every 360 ° before the intake top dead center. When started, in step S301, the engine speed Ne, the intake air amount Qa, and the O ₂ sensor output OX ₀ are determined. Read. Then, in step S302, O ₂ sensor output OX ₀ depending on whether or 0.45V rich lean determination value, the rich
Perform a lean decision.

If OX ₀ is 0.45 V or more, it is determined that the air conditioner is rich.
Then, it is determined whether the air-fuel ratio reversal flag A / F is set to rich in the previous routine, and if the flag A / F is not set to rich previously, the rich determination is made for the first time. in, in step S304, counts up the T _LR counting counter T ₂ by one. Then, to see if T ₂ is equal to or more than T _LR in step S305, if it is within T ₂ is T _LR, but directly advances to step S315 described later, when the T ₂ is equal to or larger than T _LR is flags a / F rich in step S306, also, the T _RL for counter T ₃ is set to 0 in step S307, the process proceeds to step S315 described later.

If it is determined in step S303 that the flag A / F has been set to rich in the previous routine, it is determined in step S308 that the noise is rich / lean switching noise. the _RL for counter T ₃ minus count, the process proceeds to step S315 described later.

If it is determined in step S302 that the O ₂ sensor output OX ₀ is not equal to or greater than the rich / lean determination value of 0.45 V, it is determined that the engine is lean.
In step 9, it is checked whether the flag A / F is set to lean in the previous routine. If the flag A / F is set to lean last time, the state of rich / lean switching noise is detected. In step S308, T
The counter T ₂ by subtracting the count for _LR, the process proceeds to step S315 described later.

Also, in the judgment of step S309,
If the flag A / F is not set to lean,
The first time that it has become lean determination this time, in step S311, counts up the T _RL count for counter T ₃ by one. Then, to see if T ₃ is equal to or greater than the T _RL in step S312, if it is within T ₃ is T _RL, but the process proceeds to step S315 which will be described later, when T3 is equal to or greater than the T _RL is, step Flag A in S313
/ F is set to lean, and T _LR is set in step S314.
The use counter T ₂ is set to 0, which will be described later Step S31
Go to 5.

The above is the description of the rich / rich state based on the output of the O ₂ sensor.
This is a delay process for lean reversal determination, and when this is completed, the process proceeds to steps S315 to S319 to set an air-fuel ratio feedback correction value cfb. Then, first, step S
At 315, it is determined whether or not the O ₂ sensor activation flag F is set to 1. If the flag F is set to 1, the air-fuel ratio inversion flag A / F is set to rich at step S316. See if there is.

When the flag A / F is set to rich, the process proceeds to step S317, where the predetermined value K is calculated from the previous air-fuel ratio feedback correction value cfb (n-1).
_The current correction value cfb (n) is set by subtracting _1, and the process proceeds to step S320 described later.

If it is determined in step S316 that the air-fuel ratio reversal flag A / F is not rich, the process proceeds to step S31.
8 and the previous air-fuel ratio feedback correction value cfb
(N-1) of the current by adding a predetermined value K ₁ correction value cfb
(N) is set, and the process proceeds to step S320 described below.

If the O ₂ sensor activation flag F is not set to 1 in step S 315, it means that the air-fuel feedback correction is not performed.
Proceeding to 9, the air-fuel feedback correction value cfb is set to 1.

[0039] After setting the air-fuel feedback correction value this manner, the process proceeds to step S320, the intake air amount Qa is multiplied by the coefficient K ₂ divided by the engine speed Ne, calculating the intake air charging efficiency Ce I do. And step S
At 321, Ce is multiplied by a water temperature correction value Cw, and further multiplied by an air-fuel ratio feedback correction value cfb to calculate a fuel injection amount (pulse width) T. At step S 322, an injection timing is determined and a predetermined injection timing is determined. Then, an injection pulse is output in step S323 to execute fuel injection.

In the above example, the activation determination value for the O ₂ sensor activation determination is set to a value equal to or greater than the rich / lean determination value. However, the present invention is not limited to this, and the activity determination value may be set lower than the rich / lean determination value. The predetermined time period T _A for delaying the air-fuel ratio feedback correction execution start, in the above example is set to at least the delay time T _LR rich lean inversion determination, T
_A, if a value close to T _LR, may be not more than T _LR. In particular, when the activation determination value is set to a value equal to or greater than the rich / lean determination value, it is preferable that the predetermined period T _A be set within the delay time T _LR , whereby the O ₂ sensor is sufficiently activated. The air-fuel ratio feedback correction can be started immediately after the delay time has elapsed.

Next, the execution of the air-fuel ratio feedback correction is performed after it is determined that the oxygen concentration sensor has shifted to the active state, and after the rich / lean determination actually shifts from the lean side to the rich side. An example in which the processing is started will be described with reference to FIG.

FIG. 8 is a routine for determining the activation of the O ₂ sensor by a time synchronization interrupt corresponding to the routine of FIG. 6 described above. The routine starts and reads the output OX ₀ of the O ₂ sensor in a step S401. It is checked whether the O ₂ sensor output OX ₀ is equal to or more than the activation determination value 0.55V.
If OX ₀ is not equal to or greater than 0.55 V, the process returns as it is. If OX ₀ is equal to or greater than 0.55 V, the process proceeds to step S403, and the air-fuel ratio inversion flag A according to the same fuel injection control routine as that of FIG. Check if / F is rich setting. Then, if the rich setting, it returns, if rich setting, sets the O ₂ sensor activation flag to 1 in step S404.

In this case, when the sensor output enters the active region from the inactive region at the time of starting or during the idling operation state, the air-fuel ratio feedback correction is not immediately started, but after a predetermined delay time has elapsed. It is started after the rich / lean determination is shifted from the lean side to the rich side.
Therefore, the feedback correction in the rich direction by the lean determination until the rich / lean determination is reversed to the rich side after the predetermined delay time has elapsed is eliminated, and the fluctuation of the air-fuel ratio is prevented.

Next, the air-fuel ratio feedback correction is executed after the determination that the oxygen concentration sensor has shifted to the active state, and when the output of the oxygen concentration sensor is leaner than the predetermined rich / lean determination value. An example in which the process is shifted to the rich side and started after a predetermined period has elapsed will be described with reference to FIG.

FIG. 9 shows a routine for determining the activation of the O ₂ sensor by a time synchronous interrupt corresponding to the routines of FIGS. 6 and 8, and starts. In step S 501, the output OX ₀ of the O ₂ sensor is read. In S502, it is determined whether the O ₂ sensor output OX ₀ is equal to or greater than the rich / lean determination value 0.45V. If OX ₀ is not equal to or higher than 0.45 V, the routine returns.

On the other hand, when OX ₀ is 0.45 V or more,
Proceeding to step S503, the previous O ₂ sensor output OX ₀ (n
-1) is less than 0.45 V, and if the previous time is less than 0.45 V (lean), step S50
At 4, the counter T ₄ is set to 0. Also, the last time was 0.
If it is not less than 45 V (rich),
At 505, the counter T ₄ is counted up by one.
Then, in any case, the process proceeds to step S506.

The counter T ₄ in step S506 to see whether more than a predetermined value T _B. Here, T _B is the value close to T _LR, T _B ≧ T _LR is desirable.

[0048] Then, when T ₄ is not greater than or equal to T _B, once it returns, T ₄ is equal to or greater than T _B, step S
Proceed to 507.

Then, in step S507, it is determined whether or not the O ₂ sensor output OX ₀ is equal to or more than the activation determination value 0.55 V. If it is not 0.55 V or more (inactive), the process returns as it is, and returns to 0.55 V or more. (Active)
In step S508 sets the O ₂ sensor activation flag F to 1.

In this case, when the sensor output enters the active region from the inactive region at the time of start-up or idling operation, the air-fuel ratio feedback correction is not immediately started, but the output of the oxygen concentration sensor is changed to a predetermined value. The process is started after a predetermined period elapses from the lean side to the rich side with respect to the rich / lean determination value. Therefore, after the sensor output becomes equal to or greater than the rich / lean determination value, the feedback correction in the rich direction due to the lean determination until the predetermined delay time elapses and the rich / lean determination is reversed to the rich side is suppressed, and the empty state is suppressed. Fluctuations in fuel ratio are prevented.

[0051]

According to the present invention, in the air-fuel ratio feedback control for setting a predetermined delay time for the rich / lean reversal determination and starting the air-fuel ratio feedback correction after the sensor output becomes equal to or more than the activation determination value. The air-fuel ratio feedback correction is started during a delay time from when the O ₂ sensor output shifts to the rich side or lean side to when the rich / lean determination is reversed, during which time the output of the O ₂ sensor is already on the rich side. It is possible to prevent the air-fuel ratio from being fluctuated by performing the air-fuel ratio feedback correction while maintaining the lean determination despite the shift.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of the present invention.

FIG. 2 is an overall system diagram of an engine to which the present invention is applied.

FIG. 3 is a schematic explanatory view of an engine intake system according to an example of the present invention.

FIG. 4 is a time chart of air-fuel ratio feedback control according to an example of the present invention.

FIG. 5 is a flowchart (routine executed at engine start) for executing air-fuel ratio feedback control according to an example of the present invention.

6 is a flow chart for executing the air-fuel ratio feedback control in an example of the present invention (O ₂ sensor activation determination routine executed by the time synchronization interrupt).

FIG. 7 is a flowchart (fuel injection control routine executed by interruption every 360 ° before intake top dead center) for executing the air-fuel ratio feedback control in one example of the present invention.

8 is a flow chart for executing the air-fuel ratio feedback control in another embodiment of the present invention (O ₂ sensor activation determination routine by the time synchronization interrupt).

9 is a further flow chart for executing the air-fuel ratio feedback control in another embodiment of the present invention (time synchronization interrupt by the O ₂ sensor activation determining routine).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 6 Combustion chamber 11 Intake passage 18 Fuel injection valve 21 Catalytic converter 22 Linear O ₂ sensor 33 Control unit

Claims (4)

[Claims] 1. An air-fuel ratio adjusting means for adjusting an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of an engine, an operating state detecting means for detecting a predetermined state quantity relating to an operating state of the engine, and the operating state detecting means Control amount setting means for setting a control amount of the air-fuel ratio adjusting means based on the predetermined state quantity detected by the control unit; an oxygen concentration sensor for detecting an oxygen concentration in exhaust gas of an engine; Rich / lean determination means for determining whether the air-fuel ratio of the mixture supplied to the combustion chamber of the engine is richer or leaner than the stoichiometric air-fuel ratio by comparing the output with a predetermined rich / lean determination value; Reversal delay means for setting a predetermined delay time for the rich / lean reversal determination by the rich / rich determination means; and air / fuel of the engine based on the determination after the delay by the reversal delay means. An air-fuel ratio feedback correction means for setting a predetermined air-fuel ratio feedback correction value for causing the ratio to converge to a predetermined target air-fuel ratio, and correcting the control amount with the air-fuel ratio feedback correction value An oxygen concentration sensor activity determining means for determining that the oxygen concentration sensor is in an active state when an output of the oxygen concentration sensor is equal to or greater than a predetermined activity determination value; and executing the correction by the air-fuel ratio feedback correction means. An air-fuel ratio of an engine, further comprising a correction execution delaying means for delaying the oxygen concentration sensor to start after a predetermined period has elapsed after the oxygen concentration sensor has been determined to have shifted to the active state by the oxygen concentration sensor activity determining means. Control device. 2. The engine according to claim 1, wherein the predetermined activity determination value is set to a value equal to or greater than the predetermined rich / lean determination value, and the predetermined period is set within the predetermined delay time. Air-fuel ratio control device. 3. An air-fuel ratio adjusting means for adjusting an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of an engine; an operating state detecting means for detecting a predetermined state quantity relating to an operating state of the engine; Control amount setting means for setting a control amount of the air-fuel ratio adjusting means based on the predetermined state quantity detected by the control unit; an oxygen concentration sensor for detecting an oxygen concentration in exhaust gas of an engine; Rich / lean determination means for determining whether the air-fuel ratio of the mixture supplied to the combustion chamber of the engine is richer or leaner than the stoichiometric air-fuel ratio by comparing the output with a predetermined rich / lean determination value; Reversal delay means for setting a predetermined delay time for the rich / lean reversal determination by the rich / rich determination means; and air / fuel of the engine based on the determination after the delay by the reversal delay means. An air-fuel ratio feedback correction means for setting a predetermined air-fuel ratio feedback correction value for causing the ratio to converge to a predetermined target air-fuel ratio, and correcting the control amount with the air-fuel ratio feedback correction value An oxygen concentration sensor activity determining means for determining that the oxygen concentration sensor is in an active state when an output of the oxygen concentration sensor is equal to or greater than a predetermined activity determination value; and executing the correction by the air-fuel ratio feedback correction means. Delayed after the oxygen concentration sensor activity determination means determines that the oxygen concentration sensor has transitioned to the active state, and the determination after the delay by the inversion delay means has started after transition from the lean side to the rich side. An air-fuel ratio control device for an engine, comprising a correction execution delay means for causing the correction to be performed. 4. An air-fuel ratio adjusting means for adjusting an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of an engine, an operating state detecting means for detecting a predetermined state quantity relating to an operating state of the engine, and the operating state detecting means Control amount setting means for setting a control amount of the air-fuel ratio adjusting means based on the predetermined state quantity detected by the control unit; an oxygen concentration sensor for detecting an oxygen concentration in exhaust gas of an engine; Rich / lean determination means for determining whether the air-fuel ratio of the mixture supplied to the combustion chamber of the engine is richer or leaner than the stoichiometric air-fuel ratio by comparing the output with a predetermined rich / lean determination value; Reversal delay means for setting a predetermined delay time for the rich / lean reversal determination by the rich / rich determination means; and air / fuel of the engine based on the determination after the delay by the reversal delay means. An air-fuel ratio feedback correction means for setting a predetermined air-fuel ratio feedback correction value for causing the ratio to converge to a predetermined target air-fuel ratio, and correcting the control amount with the air-fuel ratio feedback correction value An oxygen concentration sensor activity determining means for determining that the oxygen concentration sensor is in an active state when an output of the oxygen concentration sensor is equal to or greater than a predetermined activity determination value; and executing the correction by the air-fuel ratio feedback correction means. After the oxygen concentration sensor activity determining means determines that the oxygen concentration sensor has transitioned to the active state, and the output of the oxygen concentration sensor is from the lean side to the rich side from the predetermined rich / lean determination value. An engine having correction execution delay means for delaying the start after a predetermined period has elapsed after the shift. The air-fuel ratio control apparatus of.